High temperature superconductors

In 1986, Bednorz and Muller synthesized a particular type of ceramicmaterial (LaBa2Cu3O7) whose transition temperature was 30 K. For thisthey were awarded the Nobel Prize in Physics in the year 1987. Laterresearchers synthesized YBa2Cu3O7 with Tc around 90 K. The successbroke the barrier of liquid nitrogen temperature of 77 K, and was asort of dream come true for many scientists. It is because liquidnitrogen is readily available in most of the places and inexpensive.All high temperature superconductors are different types of oxides ofcopper assuming perovskite crystal structure. The critical temperatureis higher for those materials which have more number of copper-oxygenlayers. The formation of supercurrents in high temperature
superconductors is direction dependent. The supercurrents are strongin the copper-oxygen planes and weak in a direction perpendicular tothe planes. In bulk materials, the grain boundary effects decreasesthe critical current value.